I think weight loss is more to do with total calories than where the calories come from. Some diets get you to do fancy arithmatic with food. It works by getting you to watch what you eat rather than by getting the arithmatic right. If you want to reduce calories reducing fat is easy 'cos it's rich in calories (and healthier too).
Protein seems to 'fill you up' more than fat and carbs, so maybe higher protein (within reason) is good?
save the planet - it's the only one with chocolate